if you are thinking of using stock heads look at these posts.

https://mustangforums.com/forum/clas...yone-help.html



https://mustangforums.com/forum/clas...tud-issue.html

And rmodel is right on with the GT40 heads.

 

sweet, thanks for the info. I think I have pretty much decided to go with either the 351w heads or gt40 heads. they are cheaper and offer a good performance increase. and yes, when I buy the parts for the rebuild I will be buying new comp valve springs also along with the cam, lifters and roller rockers.

the rear end gears are the stock gears that came in a 66 mustang. its pretty high, but im not sure on the actual ratio. but I had planned on going with something more along the lines of a 3.23 or maybe a litter lower when I got the t-5.

 

One thing to keep in mind when changing heads on a 289 is compression...The GT40 and 351 heads have bigger chambers than the 289 heads and you will lose compression and pretty much any extra gains you might have gotten throught the extra air flow....If you are building the bottom end as well go with some higher compression pistons if you will be running heads with bigger chambers..